I'm not sure if the compressor is out totally, or if it just needs freon, but the a/c is blowing warm air and not cooling. The compressor was making noise, like it was working harder, but now, the compressor doesn't turn on at all (but it will do that if out of freon, too). Am I likely looking at replacing the damn compressor, or just freon?

Well, if shes out or low of freon, the compressor will not come on. Start buy adding a can to see how it works then, before you decide you need a new compressor. You can add a can your self it is easy. Buy you one with a reusable hose that will also come with a gage. The gage will give you a reference if you have enough freon in the system. Look under your hood for a sticker which will tell you how much freon it takes. Buy you a can with more Oz. than the system takes. So you will have some left over in case you need more later. Find your compressor and follow the lines out away from it. One line which is smaller goes out to the front of the car. The other bigger line should go over to the pass side and twist and turn into a cylinder at the wall. Look on this line for a port, will have a plastic cap which will screw off to access the fitting to add freon. The hose end will clip onto this fitting and you are all set. Hope this helps Fix Ya up.